We start learning from our experiences probably before we are born. Very early, our parents teach us to learn through the shortcut of learning from them instead of having to learn from experience. Quickly, we learn to learn from other people, via language spoken word, then from written word. And because our parents seem to know a LOT from our naive, ignorant point of view, we become conditioned to adopt as our own beliefs, those of our parents.
At least that's the way I see it. Of course, there are caveats when summing up something this complex in one paragraph.
Anyway, by the time we talk, we've already been introduced to theism and don't have a lot of need to reject those beliefs.
What I am trying to say is, by the time we can even understand theism and have enough verbal skills to convey that we do or do not believe in a theistic world view, the default position is long gone.
And if you've been indoctrinated into a theistic world view and you see something like the grand canyon, you're already conditioned to believe that its beauty comes from 'God's hand' so that is your default view at that point in your life and it is supported by LOTS of other such beliefs conveyed by others so it just seems natural.